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Clients are not getting IP Address from Windows 2008 DHCP Server

    Question

  • Hi,

    Recently i have migrated DHCP from Windows 2000 server to 2008 Server with the below steps (I know they r not recommended).

    netsh dhcp server dump > DHCPConf.dmp (on WIN 2000 Server)

    Replace old server IP Address to new server ip address in DHCPConf.dmp file

    netsh exec DHCPConf.dmp (on WIN 2008 server)

    I have three DHCP Scopes configured on windows 2000 server which i am able to see with all settings in windows 2008 server but now the problem is users are only able to get IP Address from Scope1. once the Scope1 is full, users are not able to get IP Address from Scope2 or Scope3. Kindly let me know how to resolve this problem. i am not seeing any error message on DHCP Server. i have tried to enable trace (netsh dhcpclient trace enable) also on windows 7 machine but didn't find any error message in log file.

    Dhiraj

    Thursday, July 22, 2010 2:50 PM

Answers

  • DHCP doesnt work that way.  It simply will not assign addresses from the first scope then the next, etc...  When a DHCP request comes in, the DHCP server must figure out which scope to assign an IP from.  If the DHCP server has a scope that is defined for the same subnet that the DHCP server has a NIC on, it will assign it from that scope.  To assign DHCP address from another scope, it would have to have that information in the packet, specifically the GIADDR field which is poplulated by the DHCP relay agent.

    If you have multiple subnets defined on the same physical wire, it is possible to group scopes together so that you can assign addresses from more than one scope to the same segment.  To do this, you have to select more than one scope and create a "SuperScope".  With a superscope in place, the DHCP server will assign addresses from the first pool, once filled, it will begin to assign addresses from the next available pool, and so on.  The use of superscopes is not common as it is not a best practice to have a physical network segment being used by various logical subnets.  In today's networks, logical segments are placed in their own VLANs are segrated from each other. 


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    Thursday, July 22, 2010 3:12 PM

All replies

  • DHCP doesnt work that way.  It simply will not assign addresses from the first scope then the next, etc...  When a DHCP request comes in, the DHCP server must figure out which scope to assign an IP from.  If the DHCP server has a scope that is defined for the same subnet that the DHCP server has a NIC on, it will assign it from that scope.  To assign DHCP address from another scope, it would have to have that information in the packet, specifically the GIADDR field which is poplulated by the DHCP relay agent.

    If you have multiple subnets defined on the same physical wire, it is possible to group scopes together so that you can assign addresses from more than one scope to the same segment.  To do this, you have to select more than one scope and create a "SuperScope".  With a superscope in place, the DHCP server will assign addresses from the first pool, once filled, it will begin to assign addresses from the next available pool, and so on.  The use of superscopes is not common as it is not a best practice to have a physical network segment being used by various logical subnets.  In today's networks, logical segments are placed in their own VLANs are segrated from each other. 


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    Thursday, July 22, 2010 3:12 PM
  • Thanks for your reply. but then why the same is working on Windows 2000 server. on 2000 server also there are same three Scopes & users are getting IP Address from all three. currently i have stopped DHCP Service on 2008 box & everything is working on 2000 box. If above is the case, it should not work on Windows 2000 server. or there is some other settings which is getting conflict.

    Dhiraj

    Thursday, July 22, 2010 3:35 PM
  • Dhiraj,

    This is also the first I've heard of configuring DHCP in this manner. Nonetheless, since Scope 2 and 3 are not responding, have you tried to delete them and manually recreate them? Sounds like nothing to lose doing it this way.

    Ace


    Ace Fekay, MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003, Microsoft Certified Trainer, Microsoft MVP - Directory Services. This posting is provided AS-IS with no warranties or guarantees and confers no rights.
    Thursday, July 22, 2010 3:57 PM
  • OK, I think that maybe each scope that DhirajHaritwal has defined on the 2000 server is probably servicing remote subnets.  If this is the case, you have to go back to the routers that service those remote subnets and update the DHCP RELAY AGENT (or IP HELPER for Cisco gear).  The routers need to send the packets to the 2008 DHCP server.  That is probably why two out of the three scopes are working on the 2008 Box.  I have to assume that the scope that is working is probably on the same segment as the NIC for the DHCP server.  That would explain everything.

    DhirajHaritwal - please validate my theory, or if I am completely off, let us know so that we can help you.  We simply need more detailed info about your network design.

    Something for you to read regaring DHCP Relay Agents.

    The DHCP Relay Agent
    http://www.anitkb.com/2010/04/dhcp-relay-agent.html

     


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    Friday, July 23, 2010 1:55 AM
  • thanks everybody for your reply. one fact is Scope1 is from the same subnet of DHCP Server & this is only working. All these three Scopes are for local users only. Same CISCO Router is there which is working for Windows 2000 Server but having problem in Windows 2008. I can definately delete these two scopes & add them manually. but i want to find out the reason why this is happening. Is there any other trace which i can enable to client side to check where exactly it's getting dropped.

    Dhiraj

    Friday, July 23, 2010 5:02 AM
  • thanks everybody for your reply. one fact is Scope1 is from the same subnet of DHCP Server & this is only working. All these three Scopes are for local users only. Same CISCO Router is there which is working for Windows 2000 Server but having problem in Windows 2008. I can definately delete these two scopes & add them manually. but i want to find out the reason why this is happening. Is there any other trace which i can enable to client side to check where exactly it's getting dropped.

    Dhiraj


    Are all three scopes using the same subnet mask? If not, is there an IP address configured on the DHCP server's NIC that matches each scope's subnet?  How was the old machine's NIC and IPs configured?
    Ace Fekay, MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003, Microsoft Certified Trainer, Microsoft MVP - Directory Services. This posting is provided AS-IS with no warranties or guarantees and confers no rights.
    Friday, July 23, 2010 6:39 AM
  • Thanks everybody for your reply, Now the problem has been resolved. The problem was these three Scopes was in a Super Scope on Windows 2000 Server but when we dump this config & import it into Windows Server 2008, it restored only three seperate Scopes. there was no Super Scope restored on Windows Server 2008. i have manually created a Super Scope & assign these three Scopes to this Super Scope & problem has resolved.

    Dhiraj

    Friday, July 23, 2010 7:44 AM
  • Glad to hear you figured it out.

    Cheers!

    Ace


    Ace Fekay, MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003, Microsoft Certified Trainer, Microsoft MVP - Directory Services. This posting is provided AS-IS with no warranties or guarantees and confers no rights.
    Friday, July 23, 2010 1:55 PM